In order to reduce global warming, it is desired to reduce the evolution of CO2. Also a thermal power plant or the like including an apparatus provided with a boiler, a gas turbine, and the like for burning fuel is strongly required to reduce the amount of emission of CO2 contained in an exhaust gas evolved when the apparatus is operated.
In order to reduce the amount of emission of CO2 in the apparatus like this, a method is used in which CO2 contained by the exhaust gas is absorbed by bringing the exhaust gas from the boiler, the gas turbine, and the like for burning fuel into contact with an amine-based absorbing liquid (hereinafter referred to as “CO2 absorbing liquid”) (see, for example, PTL 1.).
In addition, in recent years a method has been studied for recovering CO2 from a CO2 absorbing liquid after absorbing CO2 from the exhaust gas and for storing the recovered CO2 in the ground or the like (see, for example, PTL 2 and NPL 1).
FIG. 4 shows a construction of a CO2 recovery unit 1.
In the CO2 recovery unit 1, for example, an exhaust gas 10, which is exhausted from an apparatus such as a boiler and a turbine and contains CO2, is supplied to a cooling tower 12 by a blower (not shown). The exhaust gas 10 supplied to the cooling tower 12 is cooled by a cooling water 11 in the cooling tower 12.
The exhaust gas 10, which contains CO2 and is cooled, is supplied to a lower portion of an absorption tower 14 via an exhaust gas line 13. In the absorption tower 14, a CO2 absorbing liquid 15 having alkanolamine as a base component (amine solution) is brought into countercurrent contact with the exhaust gas 10. In this way, the CO2 in the exhaust gas 10 is absorbed by the CO2 absorbing liquid 15 and the CO2 is removed from the exhaust gas 10 exhausted from the industrial apparatus. A cleaned gas 16 in which CO2 is removed is exhausted from a tower top portion 14a of the absorption tower 14.
The CO2 absorbing liquid 15 having absorbed the CO2 in the absorption tower 14 is stored in a tower bottom portion 14b and is fed to a regeneration tower 17 by a pump 25.
The CO2 absorbing liquid 15 having absorbed the CO2 (rich solution) is heated by steam generated by a reboiler 18 in the regeneration tower 17 and hence has the CO2 emitted therefrom, thereby being regenerated as a CO2 absorbing liquid 15 (lean solution) which is able to absorb CO2. The CO2 absorbing liquid 15 regenerated in this way is supplied again to the absorption tower 14 by a pump 19 via a heat exchanger 20 and a lean solution cooling device 21 and is reused.
The CO2 emitted from the CO2 absorbing liquid 15 in the regeneration tower 17 is fed to a CO2 compressing device 23 through a gas-liquid separator 22 and is compressed there and then is fed to a storage process.
By the way, just after activating the CO2 recovery unit 1 or the CO2 compressing device 23 or because of the conditions of a storage process side, the recovered carbon dioxide gas cannot be fed to the storage process in some cases. In these cases, the recovered carbon dioxide gas is vented into the atmosphere from a vent stack 30.